The traditional Digital Subscriber Line Access Multiplexer (DSLAM) is a device with complete Asynchronous Transfer Mode (ATM) framework, i.e. it is an ATM-based DSLAM. In an ATM DSLAM network construction, the model of “ATM DSLAM+ATM switching network+Broadband Access Server (BAS)” is generally adopted, a Virtual Path Identifier (VPI) is used for representing a DSLAM office direction, and a Virtual Channel Identifier (VPI) is used for representing users governed by each DSLAM. Because a device number of DSLAM is identified by the VPI, the BAS device can rapidly and accurately locate a user in broadband maintenance management. Meanwhile, because ATM devices take charge in scheduling and managing Virtual Path (VP), configuration of the ATM devices is simple and easily managed.
Being one of protocols in the Ethernet protocol group, IEEE802.1Q standard is for Virtual Local Area Network (VLAN), and it mainly defines the procedure of realizing different local networks virtually in a local network by adopting VLAN technology. When the DSLAM is used as an access device, it can provide two identifying modes, which are port-based VLAN and 802.1Q-based VLAN on the broadband access network. The port-based VLAN identifying mode is setting default VLAN ID of port according to the DSLAM device, and for the 802.1Q-based VLAN identifying mode, since the user carries its own VLAN ID, the user can set effective ports for the carried VLAN ID.
The IEEE802.1Q standard defines Ethernet message format for encapsulating VLAN ID, and the format is shown in Table 1:
TABLE 1DstMACSrcMACEtype802.1QTagEtypeDATAFCS
Here, the 4-bytes DstMAC field is destination Media Access Control (MAC) address; the 4-bytes SrcMAC field is source MAC address; the 2-bytes Etype field is used to identify type of the Ethernet identifier and its constant value is 0x8100; the 2-bytes 802.1Qtag field is tag of 802.1Q and the VLAN ID is identified by last 12 bits of this field; the 2-bytes Etype field is used to identify type of posterior DATA field; the DATA field is filled with the data region born by the Ethernet and it contains 46-1500 bytes; the FEC field is used as the checking field and is 4 bytes long.
The broadband access network is generally composed of three layers, including BAS device layer, convergence layer and broadband access device layer. Generally, the broadband access device is responsible for converging user's flow and service, and the user being converged may also carry private VLAN information. The switch in the convergence layer manages further convergence of the user's flow, and the BAS device accomplishes processing such as authentication, management and charging etc. upon access users.
FIG. 1 is a schematic diagram illustrating the procedure of broadband access network transmitting user position information in the prior art. In current broadband network construction, the Virtual Local Area Network Identifier (VLAN ID) encapsulation format specified in the IEEE 802.1Q standard is mainly adopted to map the information of port or Permanent Virtual Channel (PVC) that user accesses one by one to the 802.1Q-based Ethernet message which is for encapsulating VLAN ID, and send the position information of this user to the BAS device through the VLAN ID born by the data message itself. When finishing the user authentication, the BAS device locates the user's position, device number of the accessed DSLAM and the port of this accessed DSLAM device via the identifier of BAS device, number of single board slots and ports in the BAS device that the broadband access device connects with and the VLAN ID within the user data message. By using this technique, related value added services can be carried out, such as binding an access account number of user with the user's position, implementing the access of dedicated line subscriber, etc.
FIG. 2 is a schematic diagram illustrating the procedure of broadband access device transmitting user position information in the prior art. The broadband access device in this scheme is an IP DSLAM device, user adopts ADSL access mode, and pre-configures the corresponding relationship between port position information through which the user accesses the ADSL (i.e. number of slots and ports and PVC information), and the VLAN ID. After the user data message is imported to the user access port, it is processed by interface devices and forms an Ethernet message thereafter. Here, the processing comprises a set of procedures such as ATM message reforming and self-study for Ethernet address, etc. During the procedure of importing the user data message to the user access port, the access devices will insert a TAG header in conformity with the encapsulation format of 802.1Q into the processed Ethernet message according to the input port information and the PVC information of user. Correspondingly, according to the relationship between the VLAN ID and the port information of user and PVC information, the access device forwards the Ethernet message which is transmitted from the network side and is fit for 802.1Q, removes the TAG header encapsulated in terms of 802.1Q format and generates ATM cells on ADSL line by means of cell partition.
However, the above scheme has the following problems:
1) The user is identified via the VLAN ID carried by data message itself, and according to 802.1Q protocol, there can only be 4096 VLAN IDs at most in one BAS device. If there exists a convergent device between 2-layer network devices and 3-layer network devices, the number of users gathered together by the convergence layer devices is sometimes more than 4K (4096). And because BAS devices are located in the higher layer of network, convergence devices are usually adopted between broadband access devices and BAS devices for convergence.
2) Even in the direct connecting network structure of broadband access devices and BAS devices, with the increasing scale of single-node broadband access devices, connection modes such as cascading mode are introduced in the broadband access devices to access the network for the sake of saving direct connecting optical fibers, and thus it may occur that more than 4096 users access the network and the problem of having insufficient VLAN ID still exists.